Effects of alloying elements on microstructure,hardness, and fracture toughness of centrifugally cast high-speed steel rolls |
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Authors: | Chang Kyu Kim Yong Chan Kim Jong Il Park Sunghak Lee Nack J. Kim Jung Seung Yang |
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Affiliation: | (1) the Center for Advanced Aerospace Materials, Pohang University of Science and Technology, 790-784 Pohang, Korea;(2) the Hot Rolling Department, Pohang Iron and Steel Col., Ltd, 790-785 Pohang, Korea;(3) Present address: the Materials Science and Engineering Department, Pohang University of Science and Technology, Korea;(4) the Research and Development Department, INI Steel Company, 790-707 Pohang, Korea |
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Abstract: | A study was made of the effects of alloying elements on the microstructure, hardness, and fracture toughness of centrifugally cast high-speed steel (HSS) rolls. Particular emphasis was placed on the role of hard carbides located along solidification cell boundaries and the type of the tempered martensitic matrix. Microstructural observation, X-ray diffraction analysis, hardness and fracture-toughness measurements, and fractographic observations were conducted on the rolls. The constitution and morphology of carbides observed within the intercellular boundaries varied depending upon the predominant alloying elements that comprised them. These massive carbide formations strongly influenced the bulk material hardness and fracture toughness due to their high hardness. The effects of alloying elements were analyzed on the basis of the liquidus-surface diagram which and indicated that the proper contents of the carbon equivalent (CE), tungsten equivalent, and vanadium were 1.9 to 2.0, 10 to 11, and 5 to 6 pct, respectively. The roll material, containing a small amount of intercellular carbides and lath-type tempered martensitic matrix, had excellent fracture toughness, since carbides were well spaced. Therefore, it was suggested that the optimization of alloying elements was required to achieve the homogeneous distribution of carbides. |
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